EP1452810A1 - Method for controlling the head pressure in a transcritical refrigeration system - Google Patents

Method for controlling the head pressure in a transcritical refrigeration system Download PDF

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Publication number
EP1452810A1
EP1452810A1 EP03100509A EP03100509A EP1452810A1 EP 1452810 A1 EP1452810 A1 EP 1452810A1 EP 03100509 A EP03100509 A EP 03100509A EP 03100509 A EP03100509 A EP 03100509A EP 1452810 A1 EP1452810 A1 EP 1452810A1
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EP
European Patent Office
Prior art keywords
expansion device
compressor
head pressure
pressure
refrigerant
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03100509A
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German (de)
French (fr)
Inventor
Giorgio Paolillo
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Delphi Technologies Inc
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Delphi Technologies Inc
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Publication date
Application filed by Delphi Technologies Inc filed Critical Delphi Technologies Inc
Priority to EP03100509A priority Critical patent/EP1452810A1/en
Publication of EP1452810A1 publication Critical patent/EP1452810A1/en
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60H—ARRANGEMENTS OF HEATING, COOLING, VENTILATING OR OTHER AIR-TREATING DEVICES SPECIALLY ADAPTED FOR PASSENGER OR GOODS SPACES OF VEHICLES
    • B60H1/00—Heating, cooling or ventilating devices
    • B60H1/32—Cooling devices
    • B60H1/3204—Cooling devices using compression
    • B60H1/3225—Cooling devices using compression characterised by safety arrangements, e.g. compressor anti-seizure means or by signalling devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B41/00—Fluid-circulation arrangements
    • F25B41/30—Expansion means; Dispositions thereof
    • F25B41/31—Expansion valves
    • F25B41/34—Expansion valves with the valve member being actuated by electric means, e.g. by piezoelectric actuators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
    • F25B9/002—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant
    • F25B9/008—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant the refrigerant being carbon dioxide
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2309/00—Gas cycle refrigeration machines
    • F25B2309/06—Compression machines, plants or systems characterised by the refrigerant being carbon dioxide
    • F25B2309/061—Compression machines, plants or systems characterised by the refrigerant being carbon dioxide with cycle highest pressure above the supercritical pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2341/00—Details of ejectors not being used as compression device; Details of flow restrictors or expansion valves
    • F25B2341/06—Details of flow restrictors or expansion valves
    • F25B2341/063—Feed forward expansion valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2500/00—Problems to be solved
    • F25B2500/06—Damage
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2500/00—Problems to be solved
    • F25B2500/07—Exceeding a certain pressure value in a refrigeration component or cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2600/00—Control issues
    • F25B2600/02—Compressor control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2600/00—Control issues
    • F25B2600/25—Control of valves
    • F25B2600/2513—Expansion valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
    • F25B2700/21—Temperatures
    • F25B2700/2115—Temperatures of a compressor or the drive means therefor
    • F25B2700/21152—Temperatures of a compressor or the drive means therefor at the discharge side of the compressor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B49/00—Arrangement or mounting of control or safety devices
    • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
    • F25B49/022—Compressor control arrangements
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
    • Y02B30/70—Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Definitions

  • the present invention generally relates to a method for controlling the head pressure in a transcritical refrigeration system.
  • a compressor In transcritical refrigeration systems, in particular in CO 2 refrigeration systems, a compressor is used for compressing the refrigerant to a high pressure. From an outlet port of the compressor, the refrigerant flows via a first heat exchanger, generally referred to as gas cooler, to an expansion device where the refrigerant expands. From the expansion device the refrigerant flows via a second heat exchanger, generally referred to as evaporator, to an inlet port of the compressor, where the refrigerant is again compressed.
  • a first heat exchanger generally referred to as gas cooler
  • evaporator second heat exchanger
  • a transcritical refrigeration system operates partly below and partly above the refrigerant's critical pressure.
  • pressure is more or less independent of temperature since there is no longer any saturation condition. Pressure can therefore be freely chosen as a design variable.
  • the refrigerant Downstream from the compressor outlet, the refrigerant is cooled at mainly constant pressure in a gas cooler. The cooling gradually increases the density of the single-phase refrigerant.
  • the head pressure i.e. the pressure of refrigerant between the compressor outlet port and the expansion device
  • the head pressure is regulated by means of the expansion device.
  • Increasing and decreasing the opening of the expansion device determines the flow rate of the refrigerant through the expansion device, thereby regulating the pressure upstream of the expansion device.
  • By increasing the opening of the expansion device a greater amount of high-pressure refrigerant flows through the expansion device, thereby reducing the pressure upstream of the expansion device.
  • the head pressure is hence reduced.
  • by decreasing the opening of the expansion device a lesser amount of high-pressure refrigerant flows through the expansion device, thereby building up pressure upstream of the expansion device.
  • the head pressure is hence increased.
  • the head pressure i.e. the pressure upstream of the expansion device, can hence be regulated by controlling the opening of the expansion device.
  • the head pressure is generally kept as high as possible, without however exceeding a predetermined safe level.
  • the head pressure can rise above a "normal" level.
  • the head pressure can rise so high that the expansion device is no longer able to keep it below the predetermined safe level. Indeed, once the expansion device has reached its fully open position, the head pressure cannot be further reduced. The head pressure remains above the safe level and damage to the refrigerant lines and the gas cooler can occur.
  • Another way of ensuring that no damage can occur to any components is to declutch the compressor from the engine in more critical conditions. Declutching however has a negative effect on driveability of the car and should be avoided. Also, a loss of efficiency of the refrigeration system might occur.
  • the object of the present invention is to provide an improved method for controlling the head pressure in a transcritical refrigeration system.
  • a method for controlling the head pressure in a transcritical refrigeration system comprising a compressor, a first heat exchanger, an expansion device and a second heat exchanger connected in series in a refrigerant flow circuit, wherein the expansion device controls the head pressure.
  • the method comprises the steps of:
  • the expansion device is operated to further open or further close in order to regulate the pressure of the refrigerant upstream of the expansion device.
  • the expansion device has reached its physical limitation, i.e. once the expansion device is fully open, it can no longer further open to further reduce head pressure.
  • the stroke of the compressor which is e.g. an adjustable stroke compressor, is reduced.
  • the reduction of the stroke of the compressor entails a reduction in refrigerant being fed to the high-pressure side of the system. As the expansion device is still fully open, this leads to a reduction in refrigerant pressure between the compressor and the expansion device.
  • the reduction of stroke of the compressor does not have a noticeable effect on the engine itself.
  • the compressor is not declutched from the engine, so that a smoother running of the engine and improved driveability is achieved.
  • the present method also allows for the compressor and the expansion device to be designed for normal operation, i.e. for operation in normal driving conditions. If more extreme driving conditions, such as high ambient temperature and/or high engine speed, occur, the expansion device reduces the head pressure as far as possible, i.e. until the expansion device is fully open. In order to further reduce the head pressure, the stroke of the compressor is then reduced. Critical driving conditions do hence not need to be taken into account when designing the expansion device.
  • the head pressure is preferably detected at, or close to, an outlet port of the compressor. Close to the outlet port of the compressor, the pressure between the compressor and the expansion device is highest. Indeed, there is a small pressure drop through the gas cooler. For safety reasons, it is therefore preferable to measure the head pressure as close as possible to the outlet port of the compressor.
  • the head pressure is preferably detected by means of a pressure gauge.
  • the expansion device is preferably an electronically controlled expansion valve.
  • the predetermined safe level can be dependent on one or more of the following parameters: engine speed, ambient temperature, compressor discharge pressure, gas cooler outlet temperature.
  • the predetermined safe level can e.g. be determined using look-up tables or through closed-loop control.
  • the refrigerant to be used in the transcritical refrigeration system can be chosen in the group comprising ethylene (C 2 H 4 ), diborane (B 2 H 6 ), carbon dioxide (CO 2 ), ethane (C 2 H 6 ) and nitrogen oxide (N 2 O).
  • the transcritical refrigeration system 10 shown in Fig.1 comprises an adjustable stroke compressor 12, a gas cooler 14, an expansion device 16, preferably an electronically controlled expansion valve, and an evaporator 18 connected in series via refrigeration lines 20 such as to form a closed circuit.
  • a refrigerant in the circuit e.g. CO 2
  • CO 2 a refrigerant in the circuit
  • pressure is more or less independent of temperature since there is no longer any saturation condition. Pressure can therefore be freely chosen as a design variable.
  • From an outlet port 22 of the compressor the compressed refrigerant is led to the gas cooler 14, where the refrigerant is cooled at mainly constant pressure. The cooling gradually increases the density of the refrigerant.
  • the cooled refrigerant is led to the expansion device 16 in which the refrigerant expands and the pressure drops below the critical pressure of the refrigerant.
  • the expanded refrigerant is then led through the evaporator 18 back to the compressor 12, where it is again compressed.
  • the head pressure of the refrigerant i.e. the refrigerant pressure between the compressor 12 and the expansion device 16 is regulated by means of the expansion device 16.
  • the expansion device 16 is operated so as to further increase the opening thereof. A greater amount of high-pressure refrigerant thereby flows through the expansion device 16, and relieves the pressure upstream of the expansion device 16.
  • the expansion device 16 is operated so as to further decrease the opening thereof. A lesser amount of high-pressure refrigerant thereby flows through the expansion device 16, and the pressure upstream of the expansion device 16 builds up.
  • a pressure gauge 24 is arranged between the compressor 12 and the expansion device 16 in the high-pressure side of the system, for measuring the head pressure.
  • the pressure gauge 24 is located as close as possible to the outlet port 22 of the compressor 12.
  • a signal representative of the detected pressure is fed to a control unit 26, which analyses the received signal and controls the opening of the expansion device 16 accordingly.
  • the control unit 26 detects that the head pressure is above a predetermined level, it operates the expansion device 16 to further increase the opening thereof so as to increase the rate of flow of the refrigerant through the expansion device 16, thereby reducing the head pressure.
  • the control unit 26 detects that the head pressure is below a predetermined level, it operates the expansion device 16 to further reduce the opening thereof so as to decrease the rate of flow of the refrigerant through the expansion device 16, thereby increasing the head pressure.
  • the control unit 26 further comprises means for determining whether or not the expansion device 16 is substantially fully open. If the control unit 26 detects that the expansion device 16 is in a substantially fully open position and that the detected head pressure is too high, it controls the compressor 12 so as to reduce the stroke of the latter. By reducing the stroke of the compressor 12, the flow rate of refrigerant into the high-side of the system is reduced. If the flow rate of refrigerant out of the compressor is smaller than the flow rate of refrigerant through the expansion device, the pressure between the compressor and the expansion device is reduced.
  • control unit 26 When normal operating conditions are resumed, the refrigerant discharge is reduced.
  • the control unit 26 returns to regulating the head pressure by means of the expansion device 16 when the expansion device 16 is essentially fully open and the cooling capacity is too high, or when the compressor operates at full stroke and the head pressure falls below the predetermined safe level.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Air Conditioning Control Device (AREA)
  • Air-Conditioning For Vehicles (AREA)

Abstract

Method for controlling the head pressure in a transcritical refrigeration system (10) comprising a compressor (12), a first heat exchanger (14), an expansion device (16) and a second heat exchanger (18) connected in series in a refrigerant flow circuit, wherein the expansion device (16) controls the head pressure. According to the invention, the method comprises the steps of:
  • detecting the opening state of the expansion device (16) for determining if the expansion device (16) is substantially fully open;
  • detecting the head pressure of the refrigerant between the compressor (12) and the expansion device (16); and
  • reducing the stroke of the compressor (12) if the expansion device (16) is substantially fully open and the head pressure has reached a predetermined level.

Description

    Introduction
  • The present invention generally relates to a method for controlling the head pressure in a transcritical refrigeration system.
  • In transcritical refrigeration systems, in particular in CO2 refrigeration systems, a compressor is used for compressing the refrigerant to a high pressure. From an outlet port of the compressor, the refrigerant flows via a first heat exchanger, generally referred to as gas cooler, to an expansion device where the refrigerant expands. From the expansion device the refrigerant flows via a second heat exchanger, generally referred to as evaporator, to an inlet port of the compressor, where the refrigerant is again compressed.
  • A transcritical refrigeration system operates partly below and partly above the refrigerant's critical pressure. In the supercritical region, i.e. in the region where the pressure is above the refrigerant's critical pressure, pressure is more or less independent of temperature since there is no longer any saturation condition. Pressure can therefore be freely chosen as a design variable. Downstream from the compressor outlet, the refrigerant is cooled at mainly constant pressure in a gas cooler. The cooling gradually increases the density of the single-phase refrigerant.
  • The head pressure, i.e. the pressure of refrigerant between the compressor outlet port and the expansion device, is regulated by means of the expansion device. Increasing and decreasing the opening of the expansion device determines the flow rate of the refrigerant through the expansion device, thereby regulating the pressure upstream of the expansion device. By increasing the opening of the expansion device, a greater amount of high-pressure refrigerant flows through the expansion device, thereby reducing the pressure upstream of the expansion device. The head pressure is hence reduced. Similarly, by decreasing the opening of the expansion device, a lesser amount of high-pressure refrigerant flows through the expansion device, thereby building up pressure upstream of the expansion device. The head pressure is hence increased. The head pressure, i.e. the pressure upstream of the expansion device, can hence be regulated by controlling the opening of the expansion device.
  • For maximum cooling capacity, the head pressure is generally kept as high as possible, without however exceeding a predetermined safe level.
  • Under some more critical driving conditions, e.g. at high ambient temperature and/or at high engine speeds, the head pressure can rise above a "normal" level. The head pressure can rise so high that the expansion device is no longer able to keep it below the predetermined safe level. Indeed, once the expansion device has reached its fully open position, the head pressure cannot be further reduced. The head pressure remains above the safe level and damage to the refrigerant lines and the gas cooler can occur.
  • One way of ensuring that no damage can occur to any components is to design the expansion device to work under all conditions, even under the more critical conditions. However, due to the fact that the more critical conditions are generally relatively rare, a whole operating range of the expansion device is hardly ever used.
  • Another way of ensuring that no damage can occur to any components is to declutch the compressor from the engine in more critical conditions. Declutching however has a negative effect on driveability of the car and should be avoided. Also, a loss of efficiency of the refrigeration system might occur.
    • Object of the invention
  • The object of the present invention is to provide an improved method for controlling the head pressure in a transcritical refrigeration system.
    • General description of the invention
  • This object is achieved by a method for controlling the head pressure in a transcritical refrigeration system according to claim 1, the system comprising a compressor, a first heat exchanger, an expansion device and a second heat exchanger connected in series in a refrigerant flow circuit, wherein the expansion device controls the head pressure. According to the invention, the method comprises the steps of:
    • detecting the opening state of the expansion device for determining if the expansion device is substantially fully open;
    • detecting the head pressure of the refrigerant between the compressor and the expansion device; and
    • reducing the stroke of the compressor if the expansion device is substantially fully open and the head pressure has reached a predetermined level.
  • The expansion device is operated to further open or further close in order to regulate the pressure of the refrigerant upstream of the expansion device. However, once the expansion device has reached its physical limitation, i.e. once the expansion device is fully open, it can no longer further open to further reduce head pressure. According to the present invention, if it is detected that the expansion device is fully open and that the head pressure needs reducing, the stroke of the compressor, which is e.g. an adjustable stroke compressor, is reduced. The reduction of the stroke of the compressor entails a reduction in refrigerant being fed to the high-pressure side of the system. As the expansion device is still fully open, this leads to a reduction in refrigerant pressure between the compressor and the expansion device.
  • Only if the expansion device is not able, due to physical limitations, to further reduce head pressure, the head pressure is kept below a safe level through regulation of the stroke of the compressor. It will be appreciated that, in order to maintain maximum efficiency of the refrigeration system, regulation of the head pressure by means of stroke regulation only occurs when the expansion device is fully open.
  • Furthermore, the reduction of stroke of the compressor does not have a noticeable effect on the engine itself. The compressor is not declutched from the engine, so that a smoother running of the engine and improved driveability is achieved.
  • The present method also allows for the compressor and the expansion device to be designed for normal operation, i.e. for operation in normal driving conditions. If more extreme driving conditions, such as high ambient temperature and/or high engine speed, occur, the expansion device reduces the head pressure as far as possible, i.e. until the expansion device is fully open. In order to further reduce the head pressure, the stroke of the compressor is then reduced. Critical driving conditions do hence not need to be taken into account when designing the expansion device.
  • The head pressure is preferably detected at, or close to, an outlet port of the compressor. Close to the outlet port of the compressor, the pressure between the compressor and the expansion device is highest. Indeed, there is a small pressure drop through the gas cooler. For safety reasons, it is therefore preferable to measure the head pressure as close as possible to the outlet port of the compressor.
  • The head pressure is preferably detected by means of a pressure gauge.
  • The expansion device is preferably an electronically controlled expansion valve.
  • The predetermined safe level can be dependent on one or more of the following parameters: engine speed, ambient temperature, compressor discharge pressure, gas cooler outlet temperature. The predetermined safe level can e.g. be determined using look-up tables or through closed-loop control.
  • The refrigerant to be used in the transcritical refrigeration system can be chosen in the group comprising ethylene (C2H4), diborane (B2H6), carbon dioxide (CO2), ethane (C2H6) and nitrogen oxide (N2O).
    • Detailed description with respect to the figures
  • The present invention will be more apparent from the following description of a not limiting embodiment with reference to the attached figure 1, which schematically shows a transcritical refrigeration system.
  • The transcritical refrigeration system 10 shown in Fig.1 comprises an adjustable stroke compressor 12, a gas cooler 14, an expansion device 16, preferably an electronically controlled expansion valve, and an evaporator 18 connected in series via refrigeration lines 20 such as to form a closed circuit. A refrigerant in the circuit, e.g. CO2, is compressed by the compressor 12 to a pressure above the critical pressure of the refrigerant. In such conditions, pressure is more or less independent of temperature since there is no longer any saturation condition. Pressure can therefore be freely chosen as a design variable. From an outlet port 22 of the compressor, the compressed refrigerant is led to the gas cooler 14, where the refrigerant is cooled at mainly constant pressure. The cooling gradually increases the density of the refrigerant. From the gas cooler 14, the cooled refrigerant is led to the expansion device 16 in which the refrigerant expands and the pressure drops below the critical pressure of the refrigerant. The expanded refrigerant is then led through the evaporator 18 back to the compressor 12, where it is again compressed.
  • The head pressure of the refrigerant, i.e. the refrigerant pressure between the compressor 12 and the expansion device 16, is regulated by means of the expansion device 16. In order to reduce the head pressure, the expansion device 16 is operated so as to further increase the opening thereof. A greater amount of high-pressure refrigerant thereby flows through the expansion device 16, and relieves the pressure upstream of the expansion device 16. In order to increase the head pressure, the expansion device 16 is operated so as to further decrease the opening thereof. A lesser amount of high-pressure refrigerant thereby flows through the expansion device 16, and the pressure upstream of the expansion device 16 builds up.
  • A pressure gauge 24 is arranged between the compressor 12 and the expansion device 16 in the high-pressure side of the system, for measuring the head pressure. Preferably, the pressure gauge 24 is located as close as possible to the outlet port 22 of the compressor 12.
  • A signal representative of the detected pressure is fed to a control unit 26, which analyses the received signal and controls the opening of the expansion device 16 accordingly. When the control unit 26 detects that the head pressure is above a predetermined level, it operates the expansion device 16 to further increase the opening thereof so as to increase the rate of flow of the refrigerant through the expansion device 16, thereby reducing the head pressure. On the other hand, when the control unit 26 detects that the head pressure is below a predetermined level, it operates the expansion device 16 to further reduce the opening thereof so as to decrease the rate of flow of the refrigerant through the expansion device 16, thereby increasing the head pressure.
  • The control unit 26 further comprises means for determining whether or not the expansion device 16 is substantially fully open. If the control unit 26 detects that the expansion device 16 is in a substantially fully open position and that the detected head pressure is too high, it controls the compressor 12 so as to reduce the stroke of the latter. By reducing the stroke of the compressor 12, the flow rate of refrigerant into the high-side of the system is reduced. If the flow rate of refrigerant out of the compressor is smaller than the flow rate of refrigerant through the expansion device, the pressure between the compressor and the expansion device is reduced.
  • When normal operating conditions are resumed, the refrigerant discharge is reduced. The control unit 26 returns to regulating the head pressure by means of the expansion device 16 when the expansion device 16 is essentially fully open and the cooling capacity is too high, or when the compressor operates at full stroke and the head pressure falls below the predetermined safe level.
    • List of reference signs
    • 10
    transcritical refrigeration system
    12
    compressor
    14
    gas cooler
    16
    expansion device
    18
    evaporator
    20
    refrigeration lines
    22
    outlet port of the compressor
    24
    pressure gauge
    26
    control unit

Claims (6)

  1. Method for controlling the head pressure in a transcritical refrigeration system, said system comprising a compressor, a first heat exchanger, an expansion device and a second heat exchanger connected in series in a refrigerant flow circuit, wherein said expansion device controls said head pressure, said method comprising the steps of:
    detecting the opening state of said expansion device for determining if said expansion device is substantially fully open;
    detecting the head pressure of said refrigerant between said compressor and said expansion device; and
    reducing the stroke of said compressor if said expansion device is substantially fully open and said head pressure has reached a predetermined level.
  2. Method according to any of the previous claims, wherein said head pressure is detected at, or close to, an outlet port of said compressor.
  3. Method according to any of the previous claims, wherein said head pressure is detected by means of a pressure gauge.
  4. Method according to any of the previous claims, wherein said expansion device is an electronically controlled expansion valve.
  5. Method according to any of the previous claims, wherein said predetermined safe level is dependent on one or more of the following parameters:
    engine speed, ambient temperature, compressor discharge pressure, gas cooler outlet temperature.
  6. Method according to any of the previous claims, wherein said refrigerant is chosen in the group comprising:
    ethylene (C2H4), diborane (B2H6), carbon dioxide (CO2), ethane (C2H6) and
    nitrogen oxide (N2O).
EP03100509A 2003-02-28 2003-02-28 Method for controlling the head pressure in a transcritical refrigeration system Withdrawn EP1452810A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP03100509A EP1452810A1 (en) 2003-02-28 2003-02-28 Method for controlling the head pressure in a transcritical refrigeration system

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP03100509A EP1452810A1 (en) 2003-02-28 2003-02-28 Method for controlling the head pressure in a transcritical refrigeration system

Publications (1)

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EP1452810A1 true EP1452810A1 (en) 2004-09-01

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WO2011056371A3 (en) * 2009-11-03 2011-08-18 Carrier Corporation Pressure spike reduction for refrigerant systems incorporating a microchannel heat exchanger
EP3244143A1 (en) * 2016-05-13 2017-11-15 Liebherr-Transportation Systems GmbH & Co. KG Cooling device
US12613048B2 (en) 2020-01-31 2026-04-28 Carrier Corporation Refrigeration system

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WO2011056371A3 (en) * 2009-11-03 2011-08-18 Carrier Corporation Pressure spike reduction for refrigerant systems incorporating a microchannel heat exchanger
CN102575890A (en) * 2009-11-03 2012-07-11 开利公司 Pressure spike reduction for refrigerant systems incorporating a microchannel heat exchanger
CN102575890B (en) * 2009-11-03 2015-08-26 开利公司 Pressure spike in conjunction with the refrigerant system of micro channel heat exchanger reduces
US10107535B2 (en) 2009-11-03 2018-10-23 Carrier Corporation Pressure spike reduction for refrigerant systems incorporating a microchannel heat exchanger
EP3244143A1 (en) * 2016-05-13 2017-11-15 Liebherr-Transportation Systems GmbH & Co. KG Cooling device
US12613048B2 (en) 2020-01-31 2026-04-28 Carrier Corporation Refrigeration system

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